1. Field of the Invention
The present invention relates to shielded cases designed to inhibit the transmission of electromagnetic waves, electronic devices using the shielded cases, electronic apparatuses using the electronic devices, and methods for manufacturing the shielded cases.
2. Description of the Related Art
FIG. 10 is a perspective view of a known shielded case 10 disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2-52481.
Shielded case 10 is made of a metal or an insulative material coated with a metallic film and includes a top wall 12, a front wall 14, a rear wall 16 and a pair of side walls 18 and 20. The bottom 22 of the shielded case 10 is designed to be mounted on a circuit board and is open.
Shielded case 10 is formed by cutting a blank 24 (FIG. 3) having a predetermined shape from a single sheet of material and bending the sheet at substantially right angles along the dashed lines of FIG. 3 to form the walls 12-20. The two side walls 18, 20 are formed by half walls 18a, 18, and 20a, 20b, respectively. Each of the half walls extends from and is integral with a respective edge of the front or rear walls 14, 16.
Mating parts 18c and 18d are formed in the half walls 18a and 18b, respectively, and interlock with each other when assembled to form the side wall 18. Similarly, mating parts 20c and 20d are formed in the half walls 20a and 20b and interlock with when assembled to form the side wall 20. The half walls 18a and 18b are butt-jointed at their respective edges in such a manner that the mating parts 18c and 18d couple with each other. Similarly, the half walls 20a, 20b are butt-jointed at their respective edges in such a manner that the mating parts 20c and 20d couple with each other.
An electronic element (e.g., an oscillation circuit) which is likely to be affected by electromagnetic waves is typically housed in the shielded case to protect it from externally generated electromagnetic waves and to contain electromagnetic waves generated by the electronic element with the case.
Various types of electronic devices can be shielded using the foregoing shield. One such class of devices are sensors for determining the movement of an object (e.g., an oscillation gyro). Such sensors are subject to strong impacts which threaten the integrity of the shielded case.
The two mating pairs of half walls of the known shielded case 10 are held together by the interlocking relationship between the mating parts 18c, 18d and 20c, 20d, respectively. Because these mating parts only interlock with one another, there is a risk that they will separate when an external impact is applied to the shielded case. If this happens, a gap will be formed between the mating parts and the electronic element in the case will not be sufficiently shielded from electromagnetic waves.
One way to avoid this problem is to apply solder to the mating parts to more firmly couple them together. However, this requires an additional manufacturing step and creates a problem of environmental pollution because of the lead in the solder.
Accordingly, it is an object of the present invention to provide a shielded case in which the mating parts do not separate from each other even when an impact is applied to the shielded case.
It is another object of the present invention to provide a shielded case in which mating parts are not likely to separate from each other and in which gaps between the mating parts can be reduced without the use of solder.
To these ends, according to a first aspect of the present invention, a shielded case comprises:
a plurality of walls, at least one of the walls being formed by at least first and second separate sections which abut one another along an interface; and
one or more depressions formed in at least one of the first and second sections so as to cause at least one of said sections to expand toward the other of said sections thereby pressure-welding said first and second sections along at least part of said interface.
In the shielded case according to the present invention, half walls are firmly coupled with each other by forming depressions in the half walls, whereby the half walls are not likely to separate from each other when an impact is applied.
In the shielded case according to the present invention, the half walls can be firmly coupled with each other without using solder, whereby a product free from lead can be provided.
In the shielded case according to the present invention, the half walls are coupled with each other without gaps therebetween, whereby electromagnetic waves inside can be prevented from leaking to the outside and the outside electronic waves can be reliably shielded.
The present invention is also directed towards a shielded electronic device comprising:
(A) a shielded case comprising:
(1) a plurality of walls, at least one of the walls being formed by at least first and second separate sections which abut one another along an interface; and
(2) one or more depression formed in at least one of the first and second sections so as to cause at least one of said sections to expand toward the other of said sections thereby pressure-welding said first and second sections along at least part of said interface; and
(B) an electronic component located in said shielded case.
In the electronic device according to the present invention, half walls of a shielded case are firmly coupled with each other, whereby a risk in that the sidewalls remove from each other and an electronic element received in the shielded case is exposed to the outside when an impact is applied is avoided.
An electronic circuit according to the present invention contains a plurality of components, at least one of said components being a shielded electronic device comprising:
(A) a shielded case comprising:
(1) a plurality of walls, at least one of the walls being formed by at least first and second separate sections which abut one another along an interface; and
(2) one or more depression formed in at least one of the first and second sections so as to cause at least one of said sections to expand toward the other of said sections thereby pressure-welding said first and second sections along at least part of said interface; and
(B) an electronic component located in said shielded case.
In the electronic apparatus according to the present invention, an electronic device is used, in which a risk that the half walls of a shielded case will separate from each other and expose an electronic element received in the shielded case to external electromagnetic radiation when an impact is applied to the case is avoided.
According to the method of the present invention, a method for manufacturing a shielded electronic device comprises:
forming a wall by bending first and second separate sections of a flat plate toward one another with opposed edges of said first and second sections abutting one another; and
forming one or more depressions in said wall so that at least one of the first and second sections is expanded toward the other along an interface between said sections to pressure weld said sections together.